The present invention relates to sanitary absorbent articles such as feminine sanitary napkins and incontinence pads, and, more particularly, to sanitary absorbent articles having a flange seal that is resistant to tearing.
Sanitary absorbent articles are, generally, large-scale commercially manufactured articles used to absorb and retain bodily exudates. Such articles are convenient in that they are often economical yet disposable; they include sanitary napkins, infant diapers, adult incontinence pads and the like.
The technology surrounding sanitary absorbent articles, and particularly feminine sanitary napkins, has undergone several advances over the past two decades. One of such advances was the addition of a flap projecting laterally from each longitudinal side of the article when the article is in a flattened state. Such flaps may be comprised of integral extensions of a material from which the article is formed or, alternatively, may simply be comprised of additional material added to the article after its formation.
When such articles are in use, the flaps are folded over the edges of the wearer""s undergarment. They thus may more firmly secure the article to the undergarment, stabilize the article within the undergarment, provide an increased absorptive area for bodily exudates, and help prevent the undergarment from becoming soiled in part by protecting the side edges of the wearer""s undergarment. The flap concept has generally met with success in the marketplace, and articles with flaps of various configurations and conformations are available to the consumer.
Conventional wisdom on the part of both designers and consumers has to date dictated that flaps on absorbent articles should be maximized at their area of juncture with the main body of the article in order to provide a greater area of protection against exudate leakage over the side of the article. Hence, a very common flap configuration is an isosceles (i.e. bilaterally symmetrical) trapezoidal-shaped flap having its base adjoined with the longitudinal side portion of the main body of the article and projecting (and tapering) away therefrom to the top of the trapezoid. The size of the flap may vary from article to article.
The difficulty with absorbent articles of the trapezoidal and other conventional flap configurations is that the absorbent articles are designed and manufactured in a flat state, while in use the article should generally adopt a two- and often three-dimensional curvature in order to correctly interface with the body of the wearer. By two-dimensional curvature it is meant that the article will curve along one axis of the three-dimensional coordinate system formed by the longitudinal centerline of the article, the transverse centerline of the article, and the line perpendicular to both. By three-dimensional curvature it is meant that the article will curve along more than one axis of a three-dimensional co-ordinate system (such a system having three orthogonal axes).
As an example, where the absorbent article is a feminine sanitary napkin, and is in use, a cross-section of the article in both the sagittal plane of the wearer""s body (i.e. the longitudinal axis of the article) and the frontal or coronal plane of the wearer""s body (i.e. the transverse axis of the article) would most likely be curved. The flaps, however, are generally designed to be folded about a linear folding axis commonly located along the line of juncture of the flap with the longitudinal side of the main body of the article. The difficulty with such a linear folding axis is that the edges of the wearer""s undergarment, about which the flaps are folded, are curved. Moreover, the undergarment edges usually contain an elastic material for snugly securing the undergarment about the legs of the wearer. Depending on the force exerted by the elastic material, a curved shape may be imparted to the flaps and the central portion of the main body of the article causing them to lift off the undergarment and wrinkle, or a flattened shape may be imparted to the edges of the undergarment causing them to not fit snugly against the legs of the wearer. In both cases, the comfort and efficiency of the article and its flaps are compromised. Moreover, the larger the flap, the more acute the problem. Thus while large flaps alleviate some difficulties on one hand (i.e. side leakage protection), they create problems on the other (i.e. instability and stress).
In order to alleviate the difficulties of conventional flap designs, a sanitary napkin has been proposed featuring flaps characterized by a width (dimension measured along the longitudinal axis of the sanitary napkin) that increases in a direction away from the main body of the napkin. This flap design offers a number of advantages, an important one being to securely retain the sanitary napkin to the undergarment of the wearer. Such enhanced retention is desirable because it stabilizes the sanitary napkin against the body of the wearer and thus reduces the likelihood of failure events.
It has been observed, however, that such strong attachment ability of the flaps may cause the flaps to tear apart from the main body when the sanitary napkin is removed from the undergarment. Usually, the wearer will not detach the flaps from the undergarment before lifting away the main body. The tendency is to simply pull the main body while the flaps remain attached to the undergarment. This manipulation creates stress levels on the sanitary napkin at the area of juncture main body/flap, often causing the flaps to tear and separate from the main body. This is undesirable since the wearer must then remove the separated flap(s) in a subsequent operation that may cause annoyance.
When the sanitary napkin tears, the tear usually originates in the peripheral area of the sanitary napkin that is called the xe2x80x9cflange sealxe2x80x9d. The flange seal is an area of juncture between two component layers of the sanitary napkin. Typically, the cover layer and the liquid-impervious barrier layer of the sanitary napkin (their respective functions will be described later in this specification) are joined together to enclose, at least partially, the absorbent system of the sanitary napkin. The junction between the components that form the flange seal may be such that the components are directly united to one another or united to one another through one or more intermediate components.
Conventional manufacturing techniques employ a heat and pressure seal method that uses the application of pressure and/or heat to bond the layers of the sanitary napkin that form the flange seal. With this technique, the pressure applied on the layers forming the flange seal reduces the ability of the flange seal to resist shear stress. Without intent of being bound by a specific theory, this may be explained by the distortion that the materials of the layers forming the flange seal undergo during the heat and pressure seal operation. The high levels of pressure and heat have the effect of reducing the caliper of the layers to the point where the material is literally crushed which effectively reduces its ability to withstand shear stress.
When shear stress is applied to a flange seal formed by using a heat and pressure seal technique, having an order of magnitude observed when a sanitary napkin is removed by the wearer from the undergarment with the flaps still attached to the undergarment, it can produce a tear across the flange seal. The tear can then propagate to other components of the sanitary napkin, such as the flaps, and ultimately cause one or both flaps to separate from the main body of the sanitary napkin.
Considering this background, it clearly appears that there is a need in the industry to develop an improved flange seal for a sanitary absorbent article that can better resist shear stress by comparison to prior art flange seal configurations.
According to one broad aspect the invention provides a sanitary absorbent article comprising:
a main body, the main body having two opposing longitudinal side portions, two opposing transverse side portions, an imaginary longitudinal centerline and an imaginary transverse centerline, the main body including:
a fluid-pervious cover layer, the fluid-pervious cover layer facing towards a wearer""s body when the sanitary absorbent article is in use by the wearer;
a liquid-impervious barrier layer, the liquid-impervious barrier layer facing away from the wearer""s body when the sanitary absorbent article is in use by the wearer;
an absorbent system intermediate the fluid-pervious cover layer and the liquid-impervious barrier layer;
the fluid-pervious cover layer and the liquid-impervious barrier joined to one another to form a flange seal extending along at least a portion of the absorbent system;
at least a portion of the flange seal laying in an imaginary plane and including an outer edge and an inner edge, the inner edge residing closer to the absorbent system than the outer edge;
the portion of the flange seal laying in the imaginary plane including a first zone and a second zone separated from one another by a common boundary, an imaginary reference line laying in the imaginary plane and extending in a direction from the outer edge to the inner edge intersecting the first zone before intersecting the second zone; and
the first zone manifesting a higher resistance to shear stress than the second zone.
In a non-limiting example of implementation, the longitudinal centerline of the article is an imaginary line that extends longitudinally along the main body of the article, which is equidistant from the longitudinal side portions thereof. It will thus bisect the main body into two generally mirror image halves. As the article is worn in the pudendal region, when the article is in use by a wearer, the longitudinal centerline thereof is generally parallel to, or most commonly, lies in, the sagittal plane of the wearer. The transverse centerline is an imaginary line that extends transversally across the article, and is typically, but not always, equidistant from the transverse sides thereof. The transverse centerline is perpendicular to the longitudinal centerline. Where the article has flaps (as described below), the transverse centerline is generally the line perpendicular to the longitudinal centerline that bisects the flaps.
The article is of a laminate construction and, under one non-limiting example of implementation, will have at least three layers. The first of these layers is the cover layer. The cover layer has two major surfaces, the first is an external surface (i.e. a surface that does not face another component layer of the article), which, when the article is in use by the wearer, faces the wearer""s body. The other surface is an internal surface (i.e. a surface that faces another component layer of the article), which faces the absorbent system below. The cover layer is fluid-permeable, and thus will permit the body exudate to be absorbed by the article to pass through it into the layers below.
The absorbent system, positioned below the fluid-pervious cover layer, may comprise a single layer or multiple layers or additional structures, the primary purpose of all of which is to absorb and retain exudate. Many different absorbent systems are known in the art. The absorbent system has two major surfaces, both of which are internal surfaces, i.e. they both face other layers of the napkin. The first surface faces the fluid-pervious cover layer, the second surface faces the liquid-impervious barrier layer.
Underneath the absorbent system is the liquid-impervious barrier layer. The primary purpose of the liquid-impervious barrier layer is to prevent exudate absorbed within the napkin from egressing the absorbent article on the opposite side from which it was absorbed. The liquid-impervious barrier layer is thus impervious to liquid but could be made pervious to gases to provide breathability. The liquid-impervious barrier layer has two major surfaces, an external surface that faces the undergarment of the wearer when the napkin is in use, and an internal surface that faces the absorbent system.
Optionally, the article can be provided with a pair of flaps, one flap extending laterally from each longitudinal side portion of the main body thereof. Such flaps are flexible and are capable of being folded about the crotch portion of the undergarment of the wearer. The flaps serve several purposes, including stabilizing the article within the garment of the wearer and protecting the garment from being soiled by body exudate not absorbed and/or retained by the article.
Under the non-limiting example of implementation described above, the fluid-pervious cover layer and the liquid-impervious barrier layer are joined to one another along the periphery of the article to form a flange seal enclosing the absorbent system. It is advantageous, but not essential to the invention that the flange seal surround completely, and thus contain, the absorbent system within it. At least a portion of the flange seal includes a pair of zones separated by a common boundary, namely a first zone and a second zone, the first zone manifesting a higher degree of resistance to shear stress than the second zone. A xe2x80x9chigher degree of resistance to shear stressxe2x80x9d means that the first zone can tolerate a higher level of shear stress before tearing than the second zone.
Under the non-limiting example of implementation, the first and second zones are realized by creating on the flange seal regions distinguished from one another by the level of bonding between the fluid-pervious cover layer and the liquid-impervious barrier layer. The resistance to shear stress of a zone is dependent upon the level of bonding between the fluid-pervious cover layer and the liquid-impervious barrier layer at that zone. In particular, the inventors have observed that the resistance to shear stress varies inversely with the level of bonding achieved between the fluid-pervious cover layer and the liquid-impervious barrier layer. In a specific example of implementation, the fluid-pervious cover layer and the liquid-impervious barrier layer manifest a stronger bond at the second zone than at the first zone. The expression xe2x80x9cstronger bondxe2x80x9d or any other equivalent terminology used in this specification means that a measurable difference exists between the degree of adhesion established between the fluid-pervious cover layer and the liquid-impervious barrier layer. This definition does not imply that the fluid-pervious cover layer and the liquid-impervious barrier layer are necessarily bonded to one another at both zones. Rather, embodiments where an actual bond between the fluid-pervious cover layer and the liquid-impervious barrier layer exists only in the second zone, while the fluid-pervious cover layer and the liquid-impervious barrier layer are unadhered to one another in the first zone, fall under the present inventive concept. Also note that the expression xe2x80x9cfluid-pervious cover layer bonded to the liquid-impervious barrier layerxe2x80x9d or any other equivalent terminology implies a direct bond between the fluid-pervious cover layer and the liquid-impervious barrier layer or a bond through one or more intermediate components.
The present invention covers realizations where the first and the second zones extend only over a limited portion of the flange seal. In a non-limiting example of implementation, the first zone and the second zone can be formed at portions of the flange seal that in use are subjected to significant levels of sheer stress and where protection against tearing is desired. When the sanitary absorbent article is a sanitary napkin, such portions can be the segments of the flange seal adjoining the juncture areas between the flaps and the main body. In another broad aspect, the invention also provides a sanitary absorbent article, comprising:
a first layer of material;
a second layer of material;
a flange seal at which the first layer of material is attached to the second layer of material in an overlapping relationship,
at least a portion of the flange seal laying in an imaginary plane and including a first edge portion and a second edge portion in a spaced apart relationship to the first edge portion;
the portion of the flange seal laying in the imaginary plane including a first zone and a second zone separated from one another by a common boundary, an imaginary reference line laying in the imaginary plane and extending in a direction from the first edge portion to the second edge portion intersecting the first zone before said second zone; and
the first zone manifesting a higher resistance to shear stress than the second zone.
In a yet another broad aspect the invention also provides a sanitary absorbent article, comprising:
a first layer of material;
a second layer of material;
a flange seal at which the first layer of material is attached to the second layer of material in an overlapping relationship,
at least a portion of the flange seal being characterized by strong bond areas separated from one another by weak bond areas, the weak bond areas being characterized by a geometrical extension along a predetermined direction.